On Thu, Jan 13, 2011 at 12:19:00PM -0500, Ryan Stone wrote: > I've been trying to get an application compiled with gcc 4.5.1 running > on FreeBSD 8.1, but it's been crashing during startup with a SIGBUS. > It turns out that the problem is that gcc is issuing SSE > instructions(in my case, a movdqa) that assume that the stack will be > aligned to a 16-byte boundary. It seems that Linux/i386 guarantees > this, and I worry that gcc has extended this assumption to all i386 > architectures. I'm assuming that FreeBSD doesn't make any such > promises based on the fact that I'm getting crashes. > > There does seem to be a flag (-mstackrealign) that you can set to > force gcc to align the stack to what it wants, but that pessimizes the > generated code a bit. Some googling would seem to indicate that > -mpreferred-stack-boundary won't always handle this problem correctly. > > Any ideas? My inclination, at least for our local source tree here at > $WORK, would be to accommodate gcc and guarantee the stack alignment > that it wants rather than pessimize our application. It seems we have > an old local patch/hack in our FreeBSD 6.1 tree(apparently based on > this: > http://www.freebsd.org/cgi/getmsg.cgi?fetch=438552+0+/usr/local/www/db/text/2000/freebsd-current/20000507.freebsd-current). > I believe that this patch is the reason why we haven't seen the > problem when running on 6.1, but the patch doesn't seem to work > anymore on 8.1.
Look at lib/csu/i386-elf/crt1_s.S, we align stack on startup.
My understanding is that the requirement is (%esp & 0xf) == 0 just before
the call to the function. And we are off by 4 (this is my fault).
Please give this a try.
diff --git a/lib/csu/i386-elf/crt1_s.S b/lib/csu/i386-elf/crt1_s.S
index d7ed0a2..17ac0e3 100644
--- a/lib/csu/i386-elf/crt1_s.S
+++ b/lib/csu/i386-elf/crt1_s.S
@@ -42,6 +42,7 @@ _start:
.cfi_def_cfa_register %ebp
andl $0xfffffff0,%esp # align stack
leal 8(%ebp),%eax
+ subl $4,%esp
pushl %eax # argv
pushl 4(%ebp) # argc
pushl %edx # rtld cleanup
pgp7aDUftFr6a.pgp
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